Photonic phased array antennas have received a lot of attention as light sources for image scanning, communication with Light Direction And Raging (LiDAR), autonomous vehicles, robots, and measuring machines. In the application areas, photonic phased array antennas require performances such as low power consumption, wide angle and high-speed scanning, high directivity, and single main lobe radiation.
A photonic phased array antenna is formed of an external light source, a coupler, a distributor, a phase controller, and an antenna. Such elements basically have structures of waveguides. A light wave supplied from the external light source is coupled with a planar integrated optical circuit through a coupler and distributed in an arrangement of a bundle of waveguides through a distributor. The distributed light waves are modulated in phase through the phase controller, then supplied to the antenna through the waveguides, and radiated to a free space.
A foregoing invention (US Patent Application No. 2014/0192394 A1) about a nanophotonics-based photonic phased array antenna has proposed a photonic phased array antenna where a phase-controlled photonic device based in a semiconductor silicon material is integrated in a form of matrix. The antenna employed in the foregoing invention is formed in a grating structure on a dielectric material film, and such a structure is utilized in most photonic phased array antennas. However, such a unit structure of grating-structured antenna occupies a large area in transverse and longitudinal directions of a bundle of waveguides. Due to this structure, in the case that a period of antenna arrangement becomes larger, there is a problem that a permissible beam scanning angle range is reduced and the number of side lobes except a main lobe increases. Furthermore, for the case of a grating structured antenna requiring a number of gratings in a direction of waveguide, there is a problem of causing a very large period in a longitudinal direction when forming a 2D array antenna.